Breathlessness and Breathing Support – By Dr. Gnana Sankaralingam
Breathing is a natural phenomenon of inhalation of air for the supply of oxygen to the body and exhalation to get rid of carbon dioxide from the body. It is under control of a center in the brain, which increases or decreases the rate as per necessity. Breathlessness or dyspnoea is a distressing situation that occurs when oxygen supply is perceived as not to be satisfactory to demand. It manifests as increased rate of breathing due to either increase in demand as in strenous exercise or due to inavailabilty of adequate amounts of oxygen to the body as in obstruction of air passage or accumulation of fluid in lungs. Oxygen is carried mainly in combination with haemoglobin, and when lacking as in Anaemia, person becomes breathless. It can also be the result of faulty heart beats, acidosis and panic attacks. It could manifest suddenly (acute) or develop gradually (chronic). Acute breathlessness can occur in those with no underlying cause or as worsening of symptom of chronic problem.
Breathing has three components: ventillation, perfusion and gas diffusion. In ventillation, air is inhaled through respiratory passage into air bags (alveoli) in the lungs and then air is exhaled out. In perfusion, blood is pumped by heart to vessels of alveoli and after oxygenation, it is taken back to the heart. These two occur simultaneously for gas exchange to take place in the alveoli. Ventillation could be defective due to blockage in the respiratory passage such as in Asthma, perfusion could be defective due to inadequate blood flow into lungs such as in heart failure and gas exchange could be defective due to alveoli becoming filled with fluid such as in pneumonia or pulmonary oedema. If one or more of these occur, it results in breathlessness. If respiratory center in brain was damaged by poisoning or head injury, breathing becomes shallow. Also in extreme cases of Asthma, initially patients make use of chest muscles but soon get exhausted and unable to expel carbon dioxide.
Breathlessness is classified as that occuring at severe activity, that occuring at moderate activity or that occuring at rest. One can feel breathless when running for a bus or exerting to an unusual extent, but to feel breathless when at rest or at gentle physical work such as walking in the house is not normal. Orthopnoea is breathing difficulty on lying down, often needing to be propped up. Those in extreme distress might not be able to converse in sentences, and even be cyanosed. Bluish discolouration or Cyanosis results due to increased content of carbon dioxide in blood either due to inability to get rid of accumulated gas, as in chronic lung disease or due to mixing of blood in heart from right side to left as in congenital heart disease. Hyperventillation presents as rapid rate of breathing due to stimulation of the brain by panic attack or drugs, where carbon dioxide is removed in large amount.
Feeling of breathlessness occurs when brain finds that lung is not functioning enough to meet the needs of body to make breathing stronger and faster trying to increase the content of air moving in and out of lungs. Brain detects it by chemical changes in blood such as low oxygen level as in asthma, high carbon dioxide level as in chronic lung diseases and too acidic (low pH) as in diabetic keto-acidosis (acidotic breathing). Receptors (sensory tissues) in carotid arteries and chest cage also play a part in regulating breathing.
Hypoxia means that there is low level of oxygen in blood due to not adequate amount of oxygen getting into body tissue. Healthy people generally have oxygen saturation level ranging from 93% to 100%. Anything below 90% is considered low but it is not unusual for chronic obstructive pulmonary disease (COPD) patients to dip below 90% at times, who despite this low oxygen level may not be breathless, as brain is conditioned to that. Also one could be extremely breathless with normal oxygen level. Hypercapnoea means that there is higher level of carbon dioxide in blood due to the inability of the lungs to get rid of it. It may occur in severe attacks of asthma or in COPD. When the patient has low level of oxygen it is termed respiratory failure and depending on the level of carbon dioxide, it is classified into type I and type 2 which determines the course of treatment the patient is given.
Acute breathlessness is treated in hospitals while chronic ones are managed in general practices. If accompanied by sudden onset of chest pain, it could be heart attack with left heart failure, pulmonary embolism (clot in major lung artery) or pneumothorax (air escape into chest cavity from lungs). Associated symptoms are cough which is protective act to keep airways patent by opening up passages or expelling foreign bodies, wheeze which is due to block in lower air passage and stridor which is due to block in upper air passage. On presentation to hospital, routine investigations are done such as pulse oximetry using finger probe, recording of pulse and blood presure, electrocardiography (ECG), blood tests for full count including haemoglobin, d-Dimer and arterial blood gas estimation and X-ray of chest. Physical examination is done to look for signs of heart failure such as swollen ankles, raised neck veins and others like paleness (anaemia) or cyanosis (oxygen lack). Lung signs include wheeze (inspiratory sound), rhonci (expiratory sound) both seen in asthma, crepitation (like rustling of leaves) which could be coarse as in pneumonia or fine at bases as in heart failure. If required CT angiogram, ECHO cardiogram and lung function test may be performed. When diagnosis is made about the cause, appropriate treatment regimen is instituted.
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Breathing support is given either by medications (orally, injected or inhaled) or by mechanical device. Medicines used are to clear airways either to dilate the air passage such as in Asthma (temporary obstruction) or chronic lung disease (permanent obstruction) or to clear the accumulated fluid in the lungs as in heart failure. Oxygen inhalation is also a form of medical therapy to increase the saturation in the blood which could be delivered at normal atmospheric pressure at 100% or varying percentages mixed with air through nasal catheter or face mask or at increased atmospheric pressure (Hyperbaric) in an air chamber. Mechanical devices that are used could be non-invasive such as CPAP, BiPAP or invasive by ventillators through endotracheal tube or tracheostomy. Intermittent positive pressure ones which are commonly used, could be volume controlled or pressure controlled. As it does not permit spontaneous breathing, patient has to be paralysed and sedated (induced coma). It is used for those with low respiratory drive, severe lung injury or circulatory instability. Normal breathing rate of a person is 12 to 16 per minute and the ventilator is adjusted to deliver at this cycle. Continuous positive airway pressure (CPAP) and Bi-level positive airway pressure (BiPAP) ones are applied to support only those who are breathing on their own.
